Bone fixation devices are useful for promoting the healing of injured or damaged vertebral bone segments caused by trauma, bone spur growth, tumor growth, or degenerative disc disease. These devices immobilize the bone segments to ensure the proper growth of new osseous tissue between the damaged segments.
Available systems and devices used on the cervical spine possess several shortcomings in both design and implantation protocols or methods. For example, distraction screws are used during disc removal and subsequent bone work and these screws are removed prior to bone plate placement. The empty bone holes created by removal of the distraction screws can interfere with proper placement of the bone screws used to anchor the plate and can lead to poor plate alignment along the long axis of the spine. This is especially problematic since the surgical steps that precede plate placement may distort the anatomical landmarks required to ensure proper plate alignment, leaving the surgeon with little guidance during plate implantation. For these reasons, bone plates are frequently placed “crooked” in the vertical plane. Correct plate placement in the vertical plane is especially important in plates intended to accommodate subsidence, since the plate preferentially permits movement along its long axis. Thus, when the vertical axis of the plate and that of the spine are not properly aligned, the plate will further worsen the alignment as the vertebral bones subside.
The empty bone holes left by the removal of the distraction screws also act as stress concentration points on the vertebral bodies, and may cause the bone to fracture. Improper plate placement and bone fractures can significantly increase the likelihood of failure and lead to severe chronic pain, neurological injury, and the need for surgical revision with a second procedure.
In view of the proceeding, it would be desirable to design an improved bone plating system and placement method. The new device should provide ease of use, reliable bone fixation, and the design should also maximize the likelihood of proper plate placement and avoid steps that weaken the vertebral bodies.